This invention relates to a suspension damper for dampening relative movement in the suspension system of a vehicle.
Modern motor vehicles have suspension systems which include suspension dampers or shock absorbers to control the relative movements of the vehicle chassis with respect to the vehicle body. These dampers commonly include a cylindrical housing and a piston assembly slidably mounted within the cylindrical housing. The cylindrical housing is commonly connected to a vehicle wheel end assembly. The piston assembly includes a piston rod which extends from the cylindrical housing and is connected to the vehicle body, and a piston plate which has two sets of apertures extending therethrough. Valve discs control communication through the apertures, permitting communication through one set of apertures during the compression strokes and through the other set of apertures during the rebound stroke. During the rebound stroke, only highly restricted communication is permitted through a bypass passage until the pressure differential across the piston is sufficient to cause the corresponding valve disc to open.
Prior art bypass passages are of two basic designs. The first is a slotted disc design in which the valve disc has a slot extending radially across the valve seat so as to allow some fluid to escape over the portion of the valve seat not covered by the disc. The other is a design in which an opening is made in the top of the wall defining the seat by coining a rectangular depression in the valve seat at the top of the wall to allow some fluid to flow through the opening under the seated valve disc. The latter design is potentially less expensive due to the simplicity of the coining process; but it has not been as successful as anticipated due to the wear and tear on the tooling creating the coined opening, which can cause inconsistency in the coined opening as well as additional manufacturing expense. In addition to being difficult to manufacture consistently, these prior art rectangular bypass passages cause turbulence which makes fluid flow through the bypass passage difficult to control and causes considerable performance variation.
According to the present invention, the required bypass passage is a continuously curved, preferably semicircular, coined depression in the rim of the wall forming a recess communicating the openings through which damping fluid flows through the piston plate, the rim forming a seat for a valve disc with the valve in its closed position. The semicircular configuration is easier to consistently fabricate with less wear on tooling as compared to the prior art rectangular coined depressions forming bypass passages. The semicircular shape also reduces turbulence in the flow of the damping fluid through the bypass passage, resulting in a controlled fluid flow and less variation in the performance of the valve discs.